Field of the Invention
The present invention refers to a brush and a method for producing same.
Brushes are normally made from an injection-molded body which carries one or several bundles of bristles. While in former times the bundle of bristles was held by a metallic anchor in a recess previously introduced into the brush head body, recent methods for producing brushes sometimes suggest that the bundle of bristles should be provided with a thickened portion shaped by melting, which in the production of the brush head body by way of injection molding is normally introduced at a distance into a mold cavity of an injection mold and fused by liquid plastic which forms the brush head body.
Although the above-described technique allows the design of very thin brush head bodies, it entails various problems that are particularly caused by hot plastic being injected at a high pressure into a not fully completed mold cavity. This requires an exact procedure because, otherwise, the liquid plastic is pressed out through a mold cavity recess through which the bundle of bristles passes.
Faced with this problem, DE 199 62 188 A1, which goes back to the applicant, suggests for instance that the thickened portion should first of all be surrounded by a first bristle carrier which is produced at a low injection pressure and may thus have a relatively poor surface quality, and that this first bristle carrier should then be enveloped with a second plastic mass that satisfies optical and hygienic requirements.
DE 10 2011 017 099 A1 discloses a method for producing a tooth brush in which a brush body is produced by way of injection molding. A perforated plate is here used that comprises holes for holding a bundle of bristles. Support elements which partly surround said holes project from the inside of the perforated plate that faces the mold cavity. The support elements are provided distributed over the circumference in relation to the hole and are arranged at a circumferential distance relative to one another. Thus, the support elements leave free spaces between them, which free spaces are to be filled by the plastic to be injected into the mold cavity. A bundle of bristles which abuts on the end sides of the support elements with a thickened portion is thus correspondingly supported during injection molding of the base body of the brush at least in sections in circumferential direction so as to form spacers formed by the melt solidifying between the support elements. In the method a thickened portion is first of all provided on the bundle of bristles by way of melting. Subsequently, the bundle of bristles is introduced into the hole until the thickened portion abuts at the end side on the support elements. The bundle of bristles is thus arranged at a predetermined distance relative to the surface of the perforated plate and thus the surface of the brush head through which the bundles of bristles passes, and the brush head is then produced during sealing of the thickened portion.
U.S. Pat. No. 6,752,949 B2 discloses a method for producing a tooth brush in which a brush body is first produced by way of injection molding, said brush body comprising a blind hole for each bundle of bristles. In a holder, bundles of bristles are held corresponding to the arrangement of the blind holes on the brush bodies.
The securing-side end of the bundles of bristles is molten. Likewise, the brush body is heated in the area of the blind holes and locally molten. Subsequently, the bundles of bristles are respectively pushed into one of the blind holes via the holder with their thickened portions formed by way of melting. The diameter of the cylindrical blind holes is here greater than the diameter of the thickened portion, so that the plastic melt produced by heating can penetrate into an annular gap between the bundle of bristles and the brush body and solidifies there and bonds the bundle of bristles to the brush body.
The bundles of bristles which project into the mold cavity further run the risk of being entrained by the plastic mass that is injected into the mold cavity, but at any rate they run the risk of being changed in their position. Normally, however, the bundles of bristles are first of all to be produced with the desired length and topography and are only then to be secured to the brush head body by way of injection molding. A change in the position of the bundle of bristles is however not acceptable. DE 199 02 129 A1, which also goes back to the applicant, suggests that the mold cavity should be provided with flow barriers that project towards the thickened portion within the mold cavity and surround the bundle of bristles partly circumferentially at its securing-side end. These flow barriers are however part of the tool and must leave open the thickened portion at least in part, so that plastic mass can also abut on the thickened portion and can pass between the future brush head body surface, through which the bundle of bristles passes, and the thickened portion to fix the bundle of bristles with the necessary pullout strength in the brush head body. DE 10 2011 017 099 A1 discloses support elements which project inwards from the mold cavity surface and on which the thickened portion abuts during injection molding. These support elements are also provided distributed over the circumference of the bundle of bristles and extend up to the thickened portion, but leave free spaces between them, so that the molten plastic can pass up to the bundle of bristles.